i am recording guitar through a Digitech rp255, USB into windows XP using audacity 2.0.3 . everything works and sounds great so far with the exception that program will not record unless the “Software play through” is on; also the monitors also will not work unless the “sw play through” is on. When playing with the “play through” on i am hearing great delay-echo types of sound accompanying the music being played, also it really messes the drum’s timing up. I would like to play guitar with the drums on the first track, but it’s not feasible to do so with the “play through” on. I can record the drums by thierself on the 1st track and overdub on the 2nd track with guitar and everything sounds great. Actually i could do a better job i think without the sounds cause by the “play through” . I can monitor my sound through a small amp coming out of the rp255. Again with the “Software play through” on, it will not record or monitor sound. any help in this matter would be greatly appreciated. BILL 
Do you like to record Internet Audio? Some of those settings fight music recording and overdubbing.
One of the first things our overdubbing tutorials do is make you do a simple, plain recording. If you can’t do that, then overdubbing will drive you nuts.
http://manual.audacityteam.org/o/man/tutorial_recording_multi_track_overdubs.html
Koz